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Mysterious fairy circles now discovered in Australia’s desert

DEEP in the Australian outback, grass-ringed circles of bare earth stretch for several hundred square kilometres across the red soil.

This is the first time these “fairy circles” have been spotted outside the Namibian desert, where they have evaded explanation for decades.

The discovery could help resolve the long-standing mystery of how they form. “It shows that the fairy circles of Namibia do not exist on their own,” says Stephan Getzin at the Helmholtz Center for Environmental Research in Leipzig, Germany.

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Getzin and his team visited the site 15 kilometres south-east of Newman, to measure the circles and analyse conditions on the ground after seeing an aerial shot of them. “From the bird’s-eye perspective the pattern becomes clear, and you see the regular features indicative of the fairy circles,” Getzin says (see picture).

So what is behind these curious formations? In Namibia, local legends have explained the circles as the footsteps of gods, burn marks from the breath of underground dragons, or even landing spots for UFOs.

More recently, however, another theory has emerged: the circles arise when the plants compete for water and nutrients, and “organise” themselves to maximise access to scarce resources. This theory suggests such circles should feature in other arid regions of the world.

The Australian rings back up this self-organisation hypothesis. Getzin’s team found few ant or termite nests within, or near, the circles and no correlation between rings and locations of the nests that did exist.

But they did find that the hard-clay soil crust within the circles was almost impermeable to rainfall – all the water pouring into this area flowed towards the periphery, where the thirsty plants await. “That gave us clear hints that the gaps serve as a source of water for the vegetation,” Getzin says.

More water around the circle edges means more biomass and roots, and that leads to the soil becoming looser. Looser soil allows more water to penetrate and feed the vegetation, creating a feedback loop supporting the plants at the edge of the circle (PNAS, doi.org/bddw).

The dominant grasses of the Triodia genus found close to the fairy circles in Australia also form other typical drought patterns such as stripes, labyrinths or spots with individual plants surrounded by bare earth. This provides strong evidence that the fairy circles also arise due to competition for water, Getzin says, though he doesn’t claim to have solved the origin of the circles just yet. “You should never claim to put an end to the mystery,” he says. “We’ve just made one significant step forward in solving the problem.”

“It’s pretty good evidence for the self-organising theory,” says Michael Cramer, a biologist at the University of Cape Town in South Africa. “There’s still a long way to go to make it conclusive, but I think the evidence is mounting.”

This article appeared in print under the headline “Mystery fairy rings hint at their source”